Corrosion, particularly of ferrous metals, in crude oil producing, collection and refining systems is a significant problem. The adverse effects of corrosion which shorten equipment life and increase downtime have multiplied as the refinery process has expanded and become more complex. Corrosion problems in a refinery operation and in particular a crude oil unit can be the result of any one or a combination of (i) the components found in the crude oil, (ii) the chemicals used in the refinery process, and (iii) the process conditions.
The inhibition of corrosion in oil and natural gas production, collection, refinery and distribution systems has been of great concern in the industry. The use of imidazolines as corrosion inhibitors has been known in the industry. For example, U.S. Pat. No. 3,629,104, Maddox, discloses a water soluble corrosion inhibitor for well fluids which consists of the normal and acid salts of substituted imidazolines and saturated aliphatic mono and dicarboxylic acids. The water soluble imidazoline salts are prepared by forming the imidazolines from a tall oil fatty acid and diethylenetriamine, and neutralizing with a dicarboxylic acid.
Similarly, U.S. Pat. No. 3,758,493, Maddox, discloses a water soluble corrosion inhibitor, particularly for ferrous metals in contact with petroliferous fluids, which comprises normal and acid salts of substituted imidazolines. The imidazolines are prepared by reacting either a tall oil fatty acid or a polymerized carboxylic acid with a polyalkylene polyamine. The imidazolines are then reacted with aliphatic saturated mono or dicarboxylic acid to form the normal and acid salts.
While the prior art use of imidazolines as a corrosion inhibitor has been commercially acceptable, specific problems do exist. For example, imidazolines have a tendency to degrade slowly upon standing to yield a sludge. Such sludge formation has been identified as a ring opening hydrolysis of the imidazoline to yield amides.
The formation of sludge due to degradation of imidazolines can be controlled by the addition of acids such as hydrochloric acid to the imidazoline or by using excess dimer-trimer acids in the preparation of the imidazolines. See J. A. Martin and W. M. Linfield, Journal of American Oil Chemical Society, 60,823-828 (1983). However, when a carboxylic acid stabilized imidazoline is formulated in an aromatic solvent and is added to a system containing naphtha/water, stabilization of the oil/water emulsion results. This is particularly a problem in refinery areas where naphtha is often used as a distillation tower reflux. While recycling of the naphtha is desirable, the water in such an emulsion can often contain corrosive species such as sulfide, ammonia, organic acids and chloride. Thus, the entrainment or emulsification of the naphtha and water can increase operating problems such as corrosion and waste disposal for units such as sour water strippers.